Process of making alumina.



UNITED sTATEs PATENT OFFICE.

CHARLES M. HALL, OF NIAGARA FALLS, NEW YORK, ASSIGNOR TO ALUMINUMCOMPANY OF AMERICA, OF NEW KENSINGTON, VANIA.

Specification of Letters Patent.

Patented May 11, 1909.

Application filed January 11, 1906. Serial No. 295,65; I

T 0 all whom it may concern:

Be it known that I, CHARLES M. HALL, of Niagara Falls, county ofNiagara, and State of New York, have invented a Process of MakingAlumina, of which the following is a specification. I

In the manufacture of alumina as heretofore most commonly practiced,bauxite has been heated in a digester with caustic soda, and sometimeswith carbonate of soda and lime, thus producing sodium aluminate whichis treated with carbonic dioxid, whereby the alumina-is precipitated,and the soda converted into a soluble carbonate. This process involvesthe use of a large amount of soda, and a considerable proportion of thismaterial is lost because it is rendered insoluble by combination withthe silica in the bauxite.

My present invention cheapens the manufacture very greatly, and byavoiding the introduction of silica in solution and mechanicalimpurities it produces a much purer product, better suited for themanufacture of aluminum than has heretofore. been made.

I have discovered that if bauxite be intimately mixed with calciumchlorid, and; heated in an atmosphere containing oxygen or steam, thecalcium chlorid will be decomposed forming chlorin, (if anatmospherecontaining oxygen is used) or hydrochloric acid (if steam isused), and an oxid ofcalcium, which 'oxid will unite with thei aluminaand silica of the bauxite, to form an aluminate and silicate of.calcium. If this product be digested with a solution of carbonate ofsoda (to which some causticsoda may be added, if desired) enoughcarbonate of soda being used to supply about sixty-two parts of Na,O toevery one hundred and two parts of A1 0 (with preferably some excess ofthe carbonate of soda), the aluminate of calcium will be decomposed,formin soluble aluminate of soda and an insolub ecarbonate of calcium.The alumina can then be-extra'cted by known methods, preferably by theuse of carbon dioxid.

In practicing my invention I prefer to use bauxite as low as possible inlSlliCBl, for the reason that a'high'silicabauxite produces to someextent an insoluble alumino calcium silicate which is not decomposed bythe after treatment with carbonate of soda and which involves a loss, asit renders a portion of the alumina insoluble. I mix the bauxite witherably calcium chlorid, preferably in the proportions of about 110 partsof calcium chlorid to 102 parts of alumina, and 110 parts of calciumchlorid to parts of the contained silica in the bauxite. The mixture ispreferably made in the form of a wet mud, so as to bring the compoundsinto intimate contact. It is then heated at a low temperature, and ispreferably briqueted so as to render it easy to treat with the steam.The heating of the mixture and its treat ment with steam or air may becarried out with any convenient form of apparatus, but I prefer touse afurnace constructed preferably like a lime kiln having a charging-'-opening at the top and a grate or other means at the base forWithdrawing the treated product, and having near the basegas inlets andair inlets. The steam may be introduced separately, or with the air orgas,

the chlorid of the alkaline earth metal, pref- Y or gas may be employedwhich will itself yield sufficient steam of itself to effect thereaction. In order to obtain the best results, I may preheat the air andgas before introducing them into the furnace, and I pass the flame andheated gases through the charge in such manner as to obtain the propertemperature, which is a bright red heat. The gases from the furnace arepreferably drawn off by a suitable induction apparatus, and are passedthrough cooling apparatus and scrubbers, which will extract the hydro-'chloric acid, care being taken to use as little water as ossible, so asto prevent unnecessary dilutionofthe acid. The mixture when withdrawnfrom the furnace will contain aluminate of calcium and silicate ofcalcium or aluminosilicate of calcium, and whenwithdrawn the mixture isheated or dlgested with a solution of carbonate of soda, either with orwithout pressure, so as to decompose the calcium aluminate and to formsoluble aluminate of soda and insolublecarbonate of calcium.

Among the advantages of my invention are that with the use of calciumchlorid which heretofore has been "regarded as a waste and valuelessproduct, I am enabled to free bauxite from its impurities, and also as avaluable by-product to obtain hydrochloric acid or chlorin. Moreover thealumina which it yields is very pure, for all the silica of the bauxitewill combine with the lime as an in soluble compound and is thereforeeasily separated,- Furthermore, the calcium aluminate which is producedby the heating of the I bauxite as above described, when treated withsoda yields a solid product which filters out very easily and thisprevents the introduction of mechanical impurities into the solution ofaluminate of soda which would contaminate the alumina with both silicaand titanic acid. Titanic acid yields titanium in the aluminum finallyproduced from the alumina, and is for some purposes a very objectionableimpurity. My invention also effects an important saving of carbonate ofsoda. In processes heretofore used much of the soda is renderedinsoluble bycombination with the silica in the bauxite and is thereforelost, but. the calcium silicate or alumino-calcium silicate which isformed in my process is very insoluble and inert and can not react withthe soda in the subsequent treatment.

Instead of using calcium chlorid alone in the admixture with bauxite, Imay employ calcium chlorid and common salt. When common salt is added tothe calcium chlorid.

, I prefer to employ them in the proportion of about 7 5 per cent. ofcalcium chlorid and 25 per cent. of common salt, and so as'to contain asmuch chlorin as though calcium chlorid alone were used. The common saltis also decomposed by steam in the presence of bauxite, though withgreater difficulty than calcium c lorid) and will thus afford means forobtaining carbonate of soda as an additional by-product of the process.The greater air alone. In this modification of my process'chlorinisprddficed in the gases and may be collected-and utilized in themanufacture of bleaching powder. And by the term atmosphere containingoxygen I include andv intend to cover an atmos here containing oxygeneither free or combined in the form of water vapor.

My process may be modified in many other ways by those skilled in theart, since 1. An improvement in the manufacture of alumina, whichconsists in the step of producing an aluniinate of calcium by heatingbauxite in an atmosphere containing oxygen in admixture with chlorid ofcalcium, substantially as described.

An improvement in the manufacture of alumina, which consists in the stepof heating a mixture ofbauxite and calcium chlorid in the presence ofsteam, substantially scribed.

. An improvement in the manufacture of alumina, which consists inproducing an aluminate of calcium by heating bauxite in an atmospherecontainin oxygen in admixture with chlorid of calcium, and thenseparating the alumina from the aluminate, substantially as described;

1 i. An improvement in the manufacture of alumina, which consists in thestep of producing an aluminate of calcium by heating bauxite in anatmosphere containing oxygen in admixture with chlorid of calcium, thecalcium chlorid being present in proper pro- ,portions to satisfy thealumina and silica of the bauxite and to produce an insoluble silicateor alumina-silicate, substantially as described.

5. An improvement in the manufacture of alumina, which consists inthe'step of producing aluminate of; calcium by heating bauxite in anatmosphere containing oxygen in admixture. with chlorid of calcium andcommon salt, substantially as described.

6-, .An improvement in the manufacture of alumina, which consists in thestep of pro ducing an aluminate of calcium by heating bauxite in anatmosphere containing oxygen in admixture with the chlorid of calcium,

andrecovering the by-product so produced, .substantially as described.

7. The improvement in the manufacture of alumina, which consists inheating a mixture of bauxite and chlorid of calciumin an atmospherecontaining oxygen and digesting the resultant roduct with a solution ofcarbonateflof so a to form aluminate of soda, and-then recovering thealumina therefrom, substantially as described. kiln-testimony whereof, Ihave hereunto set 1iiy hand, anuary 10, 1906.

CHARLES M. HALL. Witnesses:

Tnoms ,W. BAKEW'ELL,

ANNA E. WALLACE. 4

as de-'

